Script for simple finance calculations in blender?
Ben Simonds has an addon (based off work by Bassam Kurdali) that can animate text in a variety of ways. The script is available at github. There is also a short example video of what is possible.

Bassam's original script of a simple typewriter effect is somewhat simpler -

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# &lt;pep8-80 compliant&gt;
import bpy
from bpy.app.handlers import persistent

bl_info = {
    'name': 'Typewriter Text',
    'author': 'Bassam Kurdali',
    'version': (0, 1),
    'blender': (2, 65, 0),
    'location': 'Properties Editor, Text Context',
    'description': 'Typewriter Text effect',
    'url': 'http://urchn.org',
    'category': 'Text'}

"""
Typewriter Text Animation For Font Objects
"""

def uptext(text):
    '''
    slice the source text up to the character_count
    '''
    source = text.source_text
    if source in bpy.data.texts:
        text.body = bpy.data.texts[source].as_string()[:text.character_count]
    else:
        text.body = source[:text.character_count]

@persistent   
def typewriter_text_update_frame(scene):
    '''
    sadly we need this for frame change updating
    '''
    for text in scene.objects:
        if text.type == 'FONT' and text.data.use_animated_text:
            uptext(text.data)

def update_func(self, context):
    '''
    updates when changing the value
    '''
    uptext(self)

class TEXT_PT_Typewriter(bpy.types.Panel):
    '''
    Typewriter Effect Panel
    '''
    bl_label = "Typewriter Effect"
    bl_idname = "TEXT_PT_Typewriter"
    bl_space_type = 'PROPERTIES'
    bl_region_type = 'WINDOW'
    bl_context = 'data'

    @classmethod
    def poll(cls, context):
        return context.active_object and context.active_object.type == 'FONT'

    def draw_header(self, context):
        text = context.active_object.data
        layout = self.layout
        layout.prop(text, 'use_animated_text', text="")

    def draw(self, context):
        st = context.space_data
        text = context.active_object.data
        layout = self.layout
        layout.prop(text,'character_count')
        layout.prop(text,'source_text')

def register():
    '''
    addon registration function
    '''
    # create properties
    bpy.types.TextCurve.character_count = bpy.props.IntProperty(
      name="character_count",update=update_func, min=0, options={'ANIMATABLE'})
    bpy.types.TextCurve.backup_text = bpy.props.StringProperty(
      name="backup_text")
    bpy.types.TextCurve.use_animated_text = bpy.props.BoolProperty(
      name="use_animated_text", default=False)
    bpy.types.TextCurve.source_text = bpy.props.StringProperty(
      name="source_text")
    # register the module:
    bpy.utils.register_module(__name__)
    # add the frame change handler
    bpy.app.handlers.frame_change_post.append(typewriter_text_update_frame)

def unregister():
    '''
    addon unregistration function
    '''
    # remove the frame change handler
    bpy.app.handlers.frame_change_post.remove(typewriter_text_update_frame)
    # remove the properties
    # XXX but how???
    # remove the panel
    bpy.utils.unregister_module(__name__)

if __name__ == "__main__":
    register()